This invention relates to cathode ray tube display systems having a reiteration memory wherein a full raster frame of display data is stored for read-out onto the CRT at flicker-free rates and more particularly to such systems where data to be displayed is received in a first format, for example, .rho..theta., and displayed in a second format, for example, XY.
Data display systems providing flicker-free displays on CRT's have been known for many years. The Compendium of Visual Displays published in March 1967 by the Rome Air Development Center of the United States Air Force shows in its introduction a number of visual display systems including the display system in which the invention to be described below can be used and which provides the environment in which the present invention is explained. The Compendium at page X shows a display system having a buffer store, reiteration store, a data translation device in the form of a D/A converter and a transient image device in the form of a non-storage CRT. As explained in the text and known to those skilled in the art, the reiteration store, hereinafter termed a reiteration memory, has stored therein in digital form a complete frame of data to be displayed on the CRT. The stored data is read-out of the reiteration memory through the D/A converter synchonously with the drawing of the CRT raster by the use of the usual timing circuits. The buffer store simply holds new data therein until the appropriate section of the reiteration is instantaneously being addressed for read-out onto the CRT at which time the data temporarily stored in the buffer is used to up-date the reiteration store section being addressed. When the reiteration memory is read-out at rates at least of 30 times per second the result is the desired flicker-free display on a non-storage CRT.
The Compendium teaches that a number of different types of memories can be used as reiteration memories, for example, a core memory, which is known to be a type of random access memory (RAM) or a delay line, which is known to be a type of limited access memory (LAM).
In his U.S. Pat. No. 3,147,474 Kliman taught how data received in a first coordinate format can be transformed into a second coordinate format when the first data is stored into a core memory. He taught that by threading the cores with a first set of addressing wires in accordance with one coordinate format and also providing a second set of addressing wires in accordance with the desired output coordinate format then the second set of addressing wires can be easily utilized to read the data from the core memory in the desired coordinate format. In essence, Kliman simply provided two addressing means, one of which randomly addresses the memory to store the up-date data in the proper positions to be read-out by the second addressing means.
The art-described above suffers from the shortcoming that a random access reiteration memory must be used since the entry of data into the reiteration memory (or read-out if the obverse of the above described art is used) must be performed by random addressing of the memory.
With the present rapid development of new and improved, both functionally and economically, types of memories it sometimes becomes advantageous to be able to easily produce second and succeeding generations of equipments using newly developed or available memories in order to simplify the design effort in improving subsequent generation equipment. For example, at various times the state of the art is such that RAM's have certain advantages over LAM's, while at other times the state of the art advances and these advantages reverse. It is thus desirable that a universal means of converting coordinates for display systems be devised. In other words, a coordinate conversion means which can be used with either a RAM or LAM reiteration memory in the flicker-free display art would be advantageous.